This is a powerful characteristic for industrial processes that require torque-speed control. Although, the electrical installation of an ac motor-drive system is more expensive than an induction motor with a constant frequency sinusoidal power supply, the ac motordrive system can control not only the motor speed, but also can control and limit the starting torque and current, can adjust the acceleration and deceleration ramps, can maintain a constant torque for frequencies from zero to the rated frequency, and protect the motor against over voltages and over currents.