32 research outputs found
Design-Oriented Transient Stability Analysis of Grid-Connected Converters with Power Synchronization Control
The power synchronization control (PSC) has been increasingly used with
voltage-source converters (VSCs) connected to the weak ac grid. This paper
presents an in-depth analysis on the transient stability of the PSC-VSC by
means of the phase portrait. It is revealed that the PSC-VSC will maintain
synchronization with the grid as long as there are equilibrium points after the
transient disturbance. In contrast, during grid faults without any equilibrium
points, the critical clearing angle (CCA) for the PSC-VSC is identified, which
is found equal to the power angle at the unstable equilibrium point of the
post-fault operation. This fixed CCA facilitates the design of power system
protection. Moreover, it is also found that the PSC-VSC can still
re-synchronize with the grid after around one cycle of oscillation, even if the
fault-clearing angle is beyond the CCA. This feature reduces the risk of system
collapse caused by the delayed fault clearance. These findings are corroborated
by simulations and experimental tests
DQ impedance stability analysis for the power-controlled grid-connected inverter
For a grid-connected inverter requiring the ac volt- age magnitude and the active power control, both vector control and power synchronization control can be applied. The stability comparison based on the dq impedance stability analysis between both control are carried out via three factors including the grid impedance, the inner current loop and the virtual impedance. The dq impedances of the inverter based on both control are derived. The determinant of the impedance ratio is used for the stability analysis. The bode plot of the grid impedance and the inverter impedance are present to assist the stability analysis and explain their interactions. It is found that increasing the grid impedance and the cut-off frequency of the current loop stabilize the inverter with the power synchronization control, which is converse to the vector control. Furthermore, the inverter with the power synchronization control may suffer the instabilities when connecting to a strong grid. The virtual inductor and resistor are proposed to enhance the stability for the vector control and the power synchronization control respectively. The simulation validation using Matlab/Simulink is performed