Framework for reducing digital-to-analogue converter quantisation error in servo control systems

A framework for reducing the digital-to-analogue convertor (DAC) quantisation effect in servo control systems is proposed. In the framework, two compensators are used to shape the spectrum of the DAC quantisation noise. One compensator, which is an anti-windup-based compensator, not only filters out the high-frequency part of the quantisation noise, but also provides stability and performance in the presence of control saturation. The other compensator, which is a quantisation error feedback compensator, provides effective reduction of the low-frequency noise and can account for the spectral distribution of DAC quantisation noise by an optimal choice of some parameters. Theorems concerning the solvability and the stability are given. Systematic procedures to design the compensators for single-input-single-output (SISO) and multi-input-multi-output (MIMO) plants are also suggested. To validate the performance of the framework, servo control of an optical disc head is considered. Experiments indicate that the output error caused by DAC quantisation is significantly reduced.