锁相环技术在大功率电机平稳切换中的应用研究

根据感应电动机的定子电压方程和相量图,对大功率电机变频转工频所存在的问题进行了理论分析,进而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与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,转换电流小,基本上实现了电机的无冲击起动.

PLL Application Research in Smooth Transformation for Large-power Motor

According to electrical equivalent circuit and vector graph of induction motor, the problem, that exists in the course of switch from variable frequency to work frequency is discussed in theory. It is pointed out that whether the large-power motor can he switched from VF to WF lies on phase consistency between work fre- quency phase voltage and 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 deviation, thus PLL can rapidly lock frequency and phase of VVVF output voltage, and keep phase consistency between WF power supply and VF output power supply. In the industry test it is realized to successfully complete the transformation from VF to WF. As the switch current is small, non-impact switch of the large-power motor is realized.