Frequency-Divided Resistance-Emulating Control of Grid-Connected Voltage Source Rectifiers Under Unbalanced Grids

DC-link voltage pulsation is a technical challenge for grid-connected three-phase voltage source rectifiersunder unbalanced grids. To suppress dc-link voltage ripples arising from unbalanced grids, a frequency-divided resistance-emulating control strategy is proposed in this letter. According to the frequency-divided idea, the dc-link voltage control loop consists of two parts: one dedicated to regulating the average voltage and the other focused on suppressing pulsating voltage. The inner loop is synchronized based on the resistance-emulating approach. The frequency-divided resistance-emulating control offers the following advantages: grid voltage sensors are eliminated, detailed information about circuit parameters is not required, and easy to implement because only one proportional–integral controller, one quasi-proportional–resonantcontroller, and two bandpass filters are used. To sum up, the proposed method is simple, cost effective, and robust. Experiments confirm the effectiveness and performance of the proposed method.