DC-side stability analysis of grid-tied converter with different control modes based on electrical torque analysis

The DC-side stability of the grid-tied converter under different control modes is fully investigated using electrical torque analysis. The small-signal model of a single converter connected to an ideal DC bus under various control modes is formulated. Accordingly, the damping and synchronising coefficient contributed by the DC network and controllers of grid-tied converter are separately accessed using the electrical torque analysis method and the stabilising conditions of the grid-tied converter operating under different control modes are further derived. The system stability mainly corresponds with DC network dynamics under constant active power control mode. On the contrary, the grid-tied converter under constant DC-link voltage control mode has no stability problem. Generally, elevating the DC-link capacitance or decreasing the droop gain can greatly improve the stability margin reserve of the VSC-HVDC links. In addition, the control gains of the classical PQ controller are proven to have limited impacts on DC-side system stability. Finally, the results of numerical simulation prove the validity of the proposed stability analysis method and the stable boundary for the grid-tied converter with different control modes.