A data processor determines whether a composite torque command is larger than a preset torque threshold for a time interval. The composite torque command is convertible into a direct-axis current command and a quadrature-axis current command. The data processor determines whether a rotor speed of the motor is less than a preset speed threshold for the time interval. The data processor, the current adjustment module, or the current shaping module adjusts the direct-axis current command and the quadrature-axis current command to obtain a revised direct-axis current command and revised quadrature-axis current command for the time interval if the composite torque command is larger than the preset torque threshold and if the rotor speed is less than the preset speed threshold, where the revised current commands vary by the detected rotational position of the rotor to achieve a generally constant shaft torque output.