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

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