Flexible excitation system and control method therefor

A flexible excitation system, wherein the flexible excitation system comprises a plurality of groups of flexible excitation power units connected in parallel, a deexcitation circuit unit and a flexible excitation control unit;

• each flexible excitation power unit comprises a front-stage bidirectional AC-DC converter and a rear-stage bidirectional DC-DC converter;
• the front-stage bidirectional AC-DC converter is connected with the rear-stage bidirectional DC-DC converter through an intermediate DC capacitor circuit;
• a three-phase AC input side of the front-stage bidirectional AC-DC converter is an input side of the flexible excitation power unit;
• a DC output side of the rear-stage bidirectional DC-DC converter is an output side of the flexible excitation power unit;
• the input sides of the plurality of groups of flexible excitation power units are respectively configured with AC side filter reactors and AC circuit breakers connected in series, then are connected in parallel, and are connected with a three-phase AC low-voltage side of an excitation transformer, and a three-phase AC high-voltage side of the excitation transformer is connected with a generator terminal;
• the output sides of the plurality of groups of flexible excitation power units are respectively configured with DC side filter reactors and DC circuit breakers connected in series, and then are connected in parallel for output;
• the deexcitation circuit unit consists of a deexcitation switch and a deexcitation resistor circuit;
• the deexcitation resistor circuit consists of a nonlinear deexcitation resistor and a diode connected in series, and is connected across positive and negative poles of a generator excitation winding, a positive pole of the diode is connected with the negative pole of the generator excitation winding, a negative pole of the diode is connected with one end of the nonlinear deexcitation resistor, and the other end of the nonlinear deexcitation resistor is connected with the positive pole of the generator excitation winding;
• the parallel output positive poles of the plurality of groups of flexible excitation power units are connected with the positive pole of the generator excitation winding through the deexcitation switch;
• the parallel output negative poles of the plurality of groups of flexible excitation power units are connected with the negative pole of the generator excitation winding or are connected with the deexcitation switch in series and then connected with the negative pole of the generator excitation winding;
• the flexible excitation control unit is used to cooperatively control the AC circuit breakers and the DC circuit breakers of the flexible excitation power units and the deexcitation switch, so as to realize the internal fault-tolerant operation control of the flexible excitation power units;
• the flexible excitation control unit is further used to dynamically control ceiling voltage by using the fast response control ability of the flexible excitation system when terminal voltage drops, so as to improve the forced excitation output capacity of the excitation system;
• the flexible excitation control unit is further used to limit the operation state of the excitation transformer within an allowable overload operation range of equipment.