Temperature dependencies of dielectric permittivity of TlGaSe2 have been measured under various thermal cycles. Peculiarities of anomalies in temperature dependencies of dielectric permittivity corresponding to structural phase transitions at 108 and 115K are discussed. The coexistence of two different incommensurate structures in TlGaSe2 was proposed. The phase transitions at 108 and 115K are considered as commensurate lock-in transitions. As a result a new model of the structural phase transitions in TlGaSe2 has been suggested.