Research On Modular Active DC Filter Technology

In the AC/DC or DC/AC converters,there exists fluctuating power whose frequency is two times of the line frequency due to the mismatch of instantaneous power between the AC side and the DC side.The twice pulsating power component enlarges the DC bus voltage fluctuation,which will endanger the stable operation of the converter.The traditional solution is to buffer the pulsating power by parallel electrolytic capacitors on the DC bus.However,the electrolytic capacitor suffers from large volume,short lifetime and low reliability,which not only limits the lifetime of the system,but also reduces the reliability of the system.With the development of green lighting,new energy power generation,electric vehicles and other technologies,more and more occasions need to avoid the use of large capacity electrolytic capacitors.First of all,based on AC/DC circuit,this paper analyzes the causes and influence of DC bus voltage fluctuation from the perspective of instantaneous power.After reading a large amount of relevant literatures,the implementation idea,the main circuit topology and the control strategy of the realization of the electrolytic capacitor filter scheme in the AC/DC power converter at present stage are summarized,analyzed and compared.In order to guide the design of active filter to restrain the2nd fluctuation of DC bus voltage,the shared characteristics and varieties of those strategies need to be investigated.The theoretical basis of the active filter scheme to reduce the capacitive capacity is studied.Based on the above analysis,a series stacked active filter circuit is used instead of electrolytic capacitor in the on-board charging and discharging motor system of electric vehicles.Secondly,in order to restrain the 2nd power ripple,dual loop control strategy,where outer voltage loop realizes the constant voltage output and the sinusoidal input of the full-bridge Boost in the filter,while the inner current loop realizes the synchronizing of the input current of the filter to the 2nd fluctuating current of the DC bus,is adopted for the active dc filter.In order to modularize the active DC filter,A control method,where the sum of the output of the outer voltage loop and the post-differential component of the ac component of the 2nd ripple voltage on dc bus is set as the reference of the current injection filter,is proposed.Thirdly,the working principle of the series stacked active filter circuit is analyzed in detail.The key circuit parameters and control circuit design of the filter are completed.In this paper,the design of magnetic components and the selection of switching devices in filter circuit are described in detail.The design and selection of energy storage capacitor takes into account the factors such as energy density,lifetime and cost of capacitor.Finally,a series stack type active DC filter prototype is designed based on the EV charging and discharging motor,and the design scheme is analyzed and verified.First,the simulation model is built in PSIM simulation software,and the feasibility of the circuit scheme is preliminarily verified.After that,a prototype of Active DC filter based on dsPIC33EP128GS806 full digital control is built,and the experiment debugging is completed.The prototype can effectively buffer the 2nd power pulsation in the full power range.Compared with passive filter,the volume is greatly reduced.The simulation and experimental results show that the design scheme and control method are effective and feasible,and have good application value.