利用锁相环实现大功率电机变频转工频的研究

PLL Application Research in Smooth Switch for Large-power Electric Machine

针对大功率电机变频转工频所存在的问题,结合感应电动机的定子电压方程和相量图,进行了理论分析,指出大功率电机变频转工频能否成功,关键在于变频转工频的瞬时,工频电源和变频输出电源是否相位一致。并且提出在变频器内部集成锁相环,由于锁相环输入信号频率与VCO固有频率相等时,环路可消除起始偏差,因此锁相环能够迅速锁定变频器输出电压的相位和频率,保证工频电源和变频输出电源相位一致。现场工业试验成功地实现了大功率电机变频到工频的平稳切换,切换电流大大减小。

According to electrical equivalent circuit and vector graph of induction electromotor machine, discussion is made in theory about the problem, which exists in the course of switch from variable frequency to work frequency. It is pointed out that whether the large-power electromotor can be switched from VF to WF lies on phase consistency between work frequency phase voltage and corresponging variable frequency phase voltage. Furthermore it is presented that PLL is integrated inside VVVF, when the frequency of PLL input sine wave is equal to the VCO base frequency, PLL can eliminate initiative phase errors, thus PLL can rapidly lock frequency and phase of VVVF output voltage, and keep phase consistency between WF voltage and corresponding VF output voltage. In the industry test is realized to successfully complete the switch from VF to WF, the switch current greatly decrease.