Abstract: The necessity of VVVF (variable-voltage and variable-frequency) technology in variable (frequency) speed regulation systems is expounded. The limitation of online VVVF by the traditional cosine join method is analyzed. Based on the two-variable control theory, the natural non-circumfluence control method and the symmetrical cosine join method a novel method of VVVF is put forward. The particular realization method of closed loop VVVF technique with invariable output frequency is given. Finally, the test result by the novel method of VVVF is simulated and analyzed, and a good control effect of the novel method is validated.