An Insight into the Second-Harmonic Current Reduction Control Strategies in Two-Stage Converters

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Due to the components at twice the fundamental frequency of output voltage in the instantaneous output power of a two-stage single-phase inverter (TSI), the second harmonic current (SHC) is generated in the front-end dc-dc converter (FDC). To reduce the SHC, optimizing the control strategy of the FDC is an effective and costless approach. From the view of visual impedance, this paper conducts an intensive study on the SHC reduction strategies. Origin of the SHC is illustrated first. Then, the equivalent circuit models of the FDC under different control strategies are proposed to analyse the SHC propagation characteristic. The derived model can offer a better insight into how the inductor SHC is affected by the control parameters. According to the derived models, a synthesis of different control strategies is presented and the relevant parameters are listed for control design to achieve better suppression effect. The benefits and limitations of these control strategies are also discussed. Based on the proposed equivalent circuit models, several optimization methods are proposed to enhance the effect. A 1500 VA TSI prototype is built and simulated on MATLAB/Simulink, verifying the effectiveness of the proposed optimization methods. This paper is aimed to provide a guideline for the control design and control optimization of the TSIs.