Repetitive Control of a Levitated Shaft - Fpga Implementation Based on Powell-chau Filters

This paper considers high sampling rate digital control of an electromagnetically levitated shaft. Inner loop feedback and outer loop repetitive controls are realized by a Field Programmable Gate Array (FPGA) at 100 kHz rate based on considerations made on limited FPGA computing resources, numerical dynamic range, selection of word length for fixed point computation, and distribution of parallel computing. The benefit of high sampling rate feedback control is demonstrated to reduce the sensitivity peak when compared to lower sampling rate control. The repetitive control involves inverting non-minimum phase zeros and introducing linear phase low-pass filtering for establishing robust stability. These filtering tasks are realized by a modified Powell-Chau filter, which is an efficient infinite impulse response (IIR) realization of high order finite impulse response (FIR) filter. Experimental results are presented to demonstrate the effective control performance.