Aiming at the problems of excessive single-phase current and increased input current harmonics that may occur in the mining converter systems under the conditions of voltage unbalance of the underground coal mine grids, this paper takes the unidirectional three-phase three-level mining converter front rectifier as the object of research, on the basis of analysing the rectifier topology working principle and mathematical model, combined with the positive and negative sequence voltage and current double closed-loop independent control and the inner-phase voltage equalisation control strategy under the unbalanced grids, researches and proposes a three-layer control strategy combining the zero-sequence voltage feedback and the negative-sequence current feedforward control, which realises the rectifier's unit power factor operation and solves the problem of mutual-phase DC bus voltage equalisation. Finally, the Matlab/Simulink simulation is used to verify the effectiveness and feasibility of the proposed control strategy.