Robust Damping Method For Voltage Source Converter with LCL-type Filter Under Weak Grid Conditions

Power electronic converters under weak grid conditions may trigger new dynamic stability problems. Even though massive internal and external damping methods have been investigated, their system costs and robustness have not been solved in an effective way. This paper first proposes a sensorless active damping method based on the grid current feedback filter. The mid-frequency non-passive region of converters can be reduced effectively, thus system stability improvement in weak grids can be realized. Then this paper analyzes the feedback filter which may bring about additional non-passive regions in high frequency. What's more, it has a poor robustness. The residual mid-frequency non-passive region can be enlarged under converter parameter variations. Furthermore, this paper proposes a hybrid active damping method. The grid voltage is fed forward through a low pass filter. The robustness against parameter variation is greatly improved and the non-passive region in high frequency is also totally eliminated. In order to further improve the system robustness in high frequency, a simple passive damping is also added. The damping resistor is designed small to reduce the damping loss. The simulation and experimental results prove that the proposed sensorless method can realize robust damping in an economic way.