The existing phasor measurement unit(PMU)is based on fundamental synchrophasor technology and cannot meet the emerging requirements on monitoring sub-synchronous /super-synchronous harmonics. To address this issue

a new method is proposed to track sub- synchronous/super-synchronous and fundamental phasors that has improved the existing fixed-interval-sampling phasor correction algorithm. By using adaptive frequency detection

multi-modal filtering and phasor correction

the method can work out both sub-synchronous /super-synchronous harmonic and fundamental phasors precisely for a signal containing multiple non-inter harmonics with constantly changing frequencies. The principle and implementation of the method are presented

and its accuracy and anti-noise ability have been verified with test signals as well as field measured data of an actual system. This work is supported by National Natural Science Foundation of China(No. 51322701)and State Grid Corporation of China(No. SGXJ0000KXJS1500670).