A PWM converter generally includes a low-pass filter to remove the high-frequency switching currents that flow into the power grid. If the inductance of the power grid greatly increases, the response of the automatic current regulator (ACR) deteriorates. When the ACR response deteriorates, the power grid is affected by low-frequency oscillations, making the power supply unstable. A type of low-pass filter is proposed to suppress the resonance, but several problems still remain. Active dampers achieve resonance suppression without a damping resistor. However, they need additional sensors to achieve a high performance and a sensorless type becomes more sensitive to the inductance changes in the power grid. In this study, we propose an observer-based active damper to control the resonance using an LCL filter. The deterioration in the current loop's response can be prevented, even if the power grid's inductance increases, preventing low-frequency disturbances. The proposed control method is achieved without needing to tune to the corresponding power grid's inductance.

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