Dead-time Compensation in Metro Linear Motor Drive System

The three-phase motor control system mostly used the structure of three-phase full-bridge inverter. Because the full-controlled device used was not an ideal device, during the process of turning on and off, delay existed in the device. In the design of control system, to assure that the full-controlled tubes up and down of the same arm bridge do not turn on simultaneously, dead time was usually added. The addition of dead time avoided the conduction of the bridges, but, the dead time was not effective PWM control signals, it might make the control performance worse and cause torque ripple. Because the linear motor in subway was a direct drive system, it had a wide operating frequency range. The operating frequency of the most linear motors was lower compared with rotary motors. The effect of dead time to the output effective voltage vector got larger, so, dead-time compensation was important to linear motor control system. In this paper, the error dead-time voltage vector was calculated. For this system, space vector pulse width modulation (SVPWM) was used, and TMS320F2812 was used as control chip. In this research, the current waveforms before and after dead-time compensation were compared, the results which used dead-time compensation were significantly better than the other one. It was indicated that the control performance would be improved when using the dead-time compensation in linear motor drive system.