Study on effects of negative driving torque in servomotor drivers

Many applications, such as elevators, electric cars and robotic applications, require a servomotor driver capable of controlling a motor to drive its load with either positive or negative driving torque. The negative driving torque is defined as torque applied to a load in the reverse direction of motor rotation. In a servomotor driver with a switching amplifier, when the motor drives its load with negative driving torque, effects of negative driving torque might damage the servomotor driver and complicate dynamic characteristics of the servomotor system. Thus, in order to investigate effects of the negative driving torque in servomotor drivers, this paper uses the numerical simulation that combines the simulation of a control system with that of electronic circuits. The simulation results show that the negative driving torque is required for decelerating and compensating disturbance. During decelerating and compensating disturbance, the pulse-width modulation (PWM) amplifier of a servomotor driver will generate regenerative current that flows from the motor back into the power supply, and then makes the power supply voltage rise.