1.School of Electric Power, South China University of Technology, Guangzhou 510641, China;2.State Key Laboratory of HVDC (Electric Power Research Institute of China Southern Power Grid Company Limited), Guangzhou 510663, China;3.Yunnan Electric Power Dispatching and Control Center, Kunming 650011, China

The control function of the high voltage direct current (HVDC) control system to the converter is realized by synchronous firing control. This paper describes two representative synchronous firing control principles in detail from the two links of synchronizing and firing. One of them has the characteristics that harmonic filtering and unbalance processing are carried out by the prefilter in the synchronizing link, and the firing link is equal-interval firing, which is represented by the SIEMENS synchronous firing control. The other has the feature that the firing link contains auxiliary firing control and firing angle limitation, and the synchronous link has no prefilter, which is represented by the ABB synchronous firing control. Then the performances of two types of synchronous firing control are analyzed and compared under AC faults. The characteristics of two types of synchronous firing control are combined, and an improved synchronous firing control is proposed. Then its small-signal model is established. Finally, the step response simulation comparison and AC fault test are carried out. The simulation and test results verify that the improved system has a stronger ability to suppress subsequent commutation failures, and the improvement direction is corrective.