Performance evaluation of a velocity observer for accurate velocity estimation of servo motor drives

Because each of the position transducers commonly used in industry, i.e., encoders and resolvers, do not inherently measure an instantaneous velocity, some signal processing technique is generally required to improve the accuracy of velocity estimation at each sampling instant. This estimated signal is then used as the velocity feedback signal for the velocity loop control. The differential position technique commonly used in industry for velocity estimation suffers from a large quantization error and, therefore, limits the servo control loop bandwidth. This paper presents both the theoretical analysis and experimental verification of a scheme that uses a closed-loop observer for velocity estimation. The results have shown that the quantization error in the velocity feedback signal can be reduced dramatically when a closed-loop observer is used for velocity estimation. The results also shown that, at low speed, the velocity estimation could be improved with a simple compensation scheme