Aimed at the problems that the traditional power converter fault diagnosis method is poor in versatility, the additional hardware is needed, and the opencircuit devices fail in location, taking an asymmetric halfbridge power converter as the research object, the installation position of the traditional current sensor is improved, through analyzing the characteristics of the current slope under different faults, a diagnostic scheme based on the current slope is proposed. A mathematical model of fault variables is built up based on the input of logic signals, detection current and its slope taken as input by the scheme. Through the output value of the model, the open and shortcircuit faults of the power tube can be quickly located, and the diagnosis of each phase is independent of the motor phase. The number and control method are limited, and the versatility is strong; no additional hardware is required, and the diagnosis function is rich and the controller has a small burden. The scheme is valid.