Second Harmonic Current Reduction Of Cascaded Inverter With Feedforward Strategy

Cascaded inverter,consisting of a front-end dc-dc converter and a downstream single-phase inverter,has been widely used in various applications such as off-grid power supply.Since the instantaneous output power of the single-phase inverter pulsates at twice the output frequency,there will be current also pulsating at twice the output frequency,i.e.,second harmonic current,in the front-end dc-dc converter and the input power source.As a result,the conduction loss and current rating of the power switches are increased,and thus the life of the converter is degraded.The second harmonic current of the front-end dc-dc converter Inhibition is crucial.In this dissertation,a novel band-pass filter inserted inductor current feed-forward strategy is proposed and studied for the reduction of the second harmonic current in the front-end dc-dc converter of cascade inverter.The details are as follows:Firstly,the second harmonic current reduction mechanism based on virtual impedance is analyzed.A novel band-pass filter inserted inductor current feed-forward strategy(BPF-ICFFS)is proposed.The output impedance of the front-end dc-dc converter is improved by the inductor current feedforward method,thereby improving the second harmonic current reduction capability.The relationship between the amplitude and phase characteristics of the reciprocal of the transfer function of the PI regulator at the frequency of the double output voltage and the corner frequency of the regulator is analyzed.Based on this relationship,the inductor current feedforward function is simplified.This strategy can balance the second harmonic current reduction with Dynamic performance improvement.Secondly,the method of determining the virtual resistor and of the band-pass filter bandwidth in the inductor current feed-forward function is given.Based on the determined parameters,the second harmonic current suppression capability and dynamic performance analysis of the proposed BPF-ICFFS are carried out from the perspective of output impedance.The analysis results show that compared with the three virtual impedance strategies in the existing literature,the proposed BPF-ICFFS has similar dynamic performance and better second harmonic current reduction effect.Thirdly,cascaded inverter power supply was modeled using MATLAB/Simulink software,and the proposed BPF-ICFFS was verified by simulation.The simulation results show that compared with the three virtual impedance strategies in the existing literature,the proposed BPF-ICFFS has similar dynamic performance and can reduce the second harmonic current by more than 57.7%.Finally,the hardware and software design of a 10 k W cascade inverter prototype was completed.The prototype was used to verify the proposed BPF-ICFFS.The experimental results are consistent with the simulation results and theoretical analysis.The experimental results show that compared with the three virtual impedance strategies in the existing literature,the proposed BPF-ICFFS has similar dynamic performance and can reduce the second harmonic current by more than 57.7%.The above results show that the proposed BPF-ICFFS is effective for reducing the second harmonic current.