Abstract:
Aiming at the problem that the system stability of bidirectional grid connected converter in constant power control mode under weak current network will vary due to different power transmission directions, resulting in system oscillation and even instability, this paper proposes a virtual positive damping remodeling control strategy, which reshapes the negative impedance into positive impedance, enhances the system damping, and improves the stability. Firstly, the small signal model of AC side port impedance of bidirectional grid connected converter in
d-
q coordinate system is established in detail, and the differences of impedance characteristics in different power directions are analyzed. Secondly, combined with the expression of system minimum loop ratio and grid equivalent impedance, based on the Nyquist stability criterion, the effects of grid equivalent impedance and power transmission direction on system stability are analyzed. Then, the virtual positive damping remodeling control strategy of bidirectional inverter under weak current network is analyzed, modeled and analyzed. The results show that the virtual positive damping reshaping control can reshape the negative impedance into positive impedance and enhance the system damping. Moreover, even in the weak current network with large equivalent impedance, the system can maintain good bidirectional power stability. Finally, the effectiveness of the proposed strategy is verified by using the MATLAB / Simulink and low-power experimental platform.