Relay Feedback and its Variations

Suppose that a relay feedback system is stable and eventually yields limit cycles. The information contained in the limit cycles can be used for process frequency response estimation, as pioneered by Astrom and co-workers. Fundamentals are first provided in Section 5.1, followed by their refinements in the subsequent sections, which expand applicability to more scenarios. Note that in this chapter, only stationery oscillations are used for process identification while the following chapter involves relay transient response. This chapter focuses on non-parametric models while Chapter 7 addresses conversion from frequency responses to transfer function models.