Influence of Frequency Dependent Motor Resistance and Inductance on the Current Control Loop Design of Servo Drives

Servo drives in production machines are either position-, speed-, force-or torque-controlled. As the motor current is proportional to torque or force, the current control loop dynamics is crucial for all operating modes. In production machines used in the semiconductor industry, it is particularly important that the bandwidths of the control loops are continuously increased. It is thus important to take the dependency of motor resistance and inductance on frequency in control loop design into consideration. As the switching frequencies of wide-bandgap semiconductors increase, the effect becomes even more significant. This paper discusses the influence of frequency-dependent resistance and inductance on the behavior of a PI current controller. A design method for an optimized and robust current controller is then presented on this basis. Verification is performed with two completely different servo motors-a 3-phase permanent magnet synchronous motor and a high-dynamic optimized voice-coil motor.