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Power Electronic Handbook P15

A significant and very special class of industrial drives are those that are used for position control. These drives are typically called servo drives and the intelligent control of these drives is often called motion control. Some of the application areas of servo drives are machine tool servos, robotic actuator drives, electric vehicles, computer disk drives and the like. The power level for these drives usually range below 20 to 30 kW; however, drives with slightly lower control quality usually have power levels below 50 to 60 kW. Servo drives must meet several quality requirements, such as: 1. High dynamic. | 15 Servo Drives Sandor Halasz Budapest University of Technology and Economics 15.1 DC Drives 15.2 Induction Motor Drives PM Synchronous Motor Drive A significant and very special class of industrial drives are those that are used for position control. These drives are typically called servo drives and the intelligent control of these drives is often called motion control. Some of the application areas of servo drives are machine tool servos robotic actuator drives electric vehicles computer disk drives and the like. The power level for these drives usually range below 20 to 30 kW however drives with slightly lower control quality usually have power levels below 50 to 60 kW. Servo drives must meet several quality requirements such as 1. High dynamic response which can be realized only with special control schemes and special motors with a high torque inertia torque ratio 2. Smooth torque production in order to achieve smooth rotation and the elimination of position angle oscillations 3. High reliability with quick maintenance and repair 4. Robust control i.e. the ability of the drives to tolerate wide swings in load inertia or motor parameters As a result of these quality requirements the price of servo drives can be several times that of common industrial drives of the same size. The control scheme for servo drives usually consists of three subordinate loops as shown in Fig. 15.1. The first and most inner one is the current control loop. The YI transfer function of the current controller is generally chosen in such a manner that the current closed loop must have a cutoff angular frequency of co 0I 1000 r s. The second control loop referred to as the speed loop usually has a closed-loop control band width of o 0r. 300 r s. The outer loop or position control loop must accurately follow the position reference. All the control loops as a rule are proportional integral PI controllers the position controller is the only one that often employs proportional sometimes .