Second harmonic reduction strategy for two-stage inverter energy storage system with dual active bridge converter based on virtual LC series resonant circuit

The second harmonic current (SHC) caused by the instantaneous power of downstream inverter will seriously deteriorate the performance of two-stage inverter and shorten the life of energy storage device, which narrows the application prospect of two-stage inverter energy storage system (TSIESS). To reduce the SHC in TSIESS, this paper proposes a strategy of virtual LC series resonant circuit with notch filter (NF-VLCSRC). This strategy utilizes the virtual impedance technology to achieve the function of a LC series resonant circuit (LCSRC) paralleled to the intermediate DC bus capacitor of the TSIESS, so the output impedance of the DAB converter can become larger than the impedance of the DC bus capacitor at twice fundamental frequency and thus the SHC in the front-end DAB converter can be reduced effectively without power loss problem caused by the internal resistance of the actual LCSRC. Then, in order to facilitate the implementation and avoid interference of parameter mismatches on system performance, the NF is adopted to realize the VLCSRC strategy based on the frequency characteristics of the introduced virtual impedance. Theory analysis and experimental results are presented to illustrate the effectiveness of the proposed control techniques.