Emergency power support method under multi-direct-current and multi-constraint conditions

The invention provides an emergency power support method under multi-direct-current and multi-constraint conditions, and relates to the technical field of high-voltage direct-current transmission control. The method comprises the steps of measuring the frequency of an alternating-current bus and calculating a system frequency deviation value; pI controllers are arranged on the provincial domain and the extra-high voltage direct current transmission rectification side respectively, and the system frequency deviation value is input; calculating direct current liftable power according to constraint conditions of the provincial domain and the extra-high voltage direct current, and setting a result as a corresponding multi-constraint amplitude limiting value to perform amplitude limiting on the current output by the PI controller to obtain a direct current deviation value; and finally, adding the actual current subjected to the first-order low-pass filtering and the current instruction value, subtracting the curre