Digital servo control based on adaptive zero phase error tracking controller & zero phase prefilter

This paper describes an adaptive scheme based on zero phase error tracking controller (ZPETC) and zero phase prefilter (ZPF) in a digital tracking servo system. The overall system with ZPETC has the following frequency characteristics: the phase is zero for all frequencies; the gain is unity at only zero frequency and about unity for low frequencies. To improve the bandwidth of servo tracking system, then introduce a ZPF ahead of the ZPETC which realizes that: keep zero phase for all frequencies; improve gain characteristics of system. Because the parameters of closed loop system are unknown or varying, the ZPETC and ZPF are implemented in an adaptive control scheme. Simulations result on a dc servo motor with different controllers indicate that, the present adaptive ZPETC and ZPF achieve the best tracking performance where the desired output to be tracked is unknown and the parameters of plant change.