In order toS track phaseSchange of commutationSvoltage and improve the controlSprecision ofShigh voltage direct current transmissionS(HVDC)S pulse triggeringSdevice, this paper put forward an improved synchronousSfrequency doubling technology inSSphase-locked loop. Based on the PSCAD traditionalSDC transmissionSmodel, improvedSPLL in the foundation of the originalSpulse triggerScontrolSdevice, and throughSa specialSpre filteringStechnique, filter the harmonic and noiseSofScommutation line-voltagesSduring faults, and make it as the input signalSof PLL. In the commutationSvoltage overSzero offset case caused by asymmetric fault in theSACSsystem, to apply this method proposed by this paper, through the HVDC first benchmark modeSproposed by CIGRE toSsimulate and verify, this model can meet the requirement of equal intervalStrigger pulse of HVDCStransmission system polar control level completely.