High-Precision Active Suppression of DC Bias in AC Grids by Grid-Connected Power Converters

Increased dc injection from grid-connected power converters and an increased dc-bias sensitivity of recent distribution transformers require unprecedented precision in detecting and suppressing the dc bias in 0.4-kV ac grids. In this paper, an optimum design of the dc-bias sensing reactor is devised, along with a robust, simple-touse sensing algorithm that does not require calibration or tuning. The sample sensors are used as feedback devices within an experimental setup comprising a three-phase grid-connected inverter and a novel dc-bias suppression algorithm. The steady-state dc bias is suppressed below 65 μV, the level acceptable even with the most sensitive distribution transformers.