Impedance Editing Based Second Harmonic Current Reduction for New Energy Access System

In the renewable energy system, generally, the output voltage of renewable sources, such as photovoltaic (PV) and the fuel cell is relatively low and should be boosted to a high voltage first. However, there will be a large amount of second harmonic current (SHC) on the dc bus when powering the ac load. This article aims for suppressing the SHC in the front-end converter with a high-gain dc–dc converter. The accurate small-signal model of the high-gain converter considering leakage and magnetic inductance of the coupled inductor is proposed. Then, the impedance editing method is proposed to establish a second harmonic impedance in the control loop, which brings little influence on the system dynamic performance during the load transient. Even, the system dynamic performance will be improved due to the feedforward of the input current. Meanwhile, considering the system stability and SHC reduction, the detailed design method of optimal parameters for both controller and converter is presented. Importantly, zero-voltage switching (ZVS) of all dc–dc converter switches can be realized after SHC suppression. Hence, when the SHC is reduced, the system efficiency is improved as well. Finally, a 500 W two-stage single-phase inverter is fabricated and tested to verify the effectiveness and feasibility of the proposed SHC suppression methods.