1. A lead-angle control method in a motor control system, the method comprising the steps of: a) calculating and outputting an instruction current for compensating a difference between an instruction speed and a current speed by means of a speed controller; b) generating and outputting a rotating-coordinate-system instruction current component based on the instruction current by means of an instruction current generator; c) generating and outputting a stationary-coordinate-system instruction voltage component based on the rotating-coordinate-system instruction current component by means of an instruction voltage generator; d) calculating and outputting switching times applied to each switching element of an inverter based on the stationary-coordinate-system instruction voltage component by means of a space voltage vector controller; e) calculating and outputting a lead-angle compensation value by comparing the sum of effective vector application times outputted from the space voltage vector controller with a sampling period by means of a lead-angle compensator; and f) compensating a lead-angle component by adding the lead-angle component to the lead-angle compensation value.