Method for analyzing influence of excitation system on dynamic reactive power support of direct current receiving end power grid after flexibility transformation of unit

The invention discloses a method for analyzing influence of an excitation system on dynamic reactive power support of a direct-current receiving end power grid after flexibility transformation of a unit. The method comprises the following steps: establishing a corresponding excitation system mathematical model according to the structure of the excitation system; calculating an arc change voltage drop coefficient, a regulator output maximum amplitude limit, a regulator output minimum amplitude limit and an excitation system amplification factor in the excitation system mathematical model to obtain an excitation system transfer function and an excitation voltage change rule; establishing a relational expression of excitation voltage and excitation current of the flexibly modified unit, and obtaining a transient reactive power output expression of the flexibly modified unit; obtaining an AC system critical voltage corresponding to the DC commutation failure according to the high-voltage DC power transmission pro