Hybrid mode-locking in monolithic quantum dot lasers is studied experimentally and theoretically. A strong asymmetry of the locking range with respect to the passive mode locking frequency is observed. The width of this range increases linearly with the modulation amplitude for all operating parameters. Maximum locking range found is 30 MHz. The results of a numerical analysis performed using a set of five delay-differential equations taking into account carrier exchange between quantum dots and wetting layer are in agreement with experiments and indicate that a spectral filtering element could improve locking characteristics. Asymptotic analysis of the dependence of the locking range on the laser parameters is performed with the help of a more simple laser model consisting of three delay differential equations.