Steady Analysis of Output Switch and Research on Integrated PLL Control for Cycloconverter

Based on electrical equivalent circuit and stator vector diagram of induction electromotor, theoretical discussion is made about the problem of output switching for cycloconverter. It is pointed out that whether the high-power electromotor can be successfully switched from VF to WF lies on phase consistency between work frequency phase voltage and corresponding variable frequency phase voltage. Furthermore it is presented that PLL is integrated inside cycloconverter, when the frequency of PLL input sine wave is equal to the VCO base frequency, PLL can eliminate initiative deviation, thus PLL can rapidly lock frequency and phase of transducer output voltage, and keep phase consistency between WF power supply and corresponding VF output power supply. In the industry test it is realized to successfully complete the switch from VF to WF. As the switch electrical current is small, non-impact switch of the large-power electromotor is realized.